The present invention relates to a duct for feeding a fluid at high pressure and, in particular, to a duct comprising a metal tube, a tube of elastomeric material and a connector assembly for effecting a fluid-tight connection between the two tubes.
The invention is applied, preferably but not exclusively, to power-assisted steering installations in motor vehicles, to which the following description will refer without thereby implying any restriction.
Power-assisted steering installations generally comprise a circuit portion provided with a substantially rigid metal tube and a circuit portion provided with a flexible tube, in particular a tube of reinforced elastomeric material.
However, the problem arises of connecting the two types of tube while effecting a good seal under conditions of high pressure and with pulsating flow.
For this purpose there are generally used connecting assemblies comprising a tubular connector which is rigidly fixed, for example welded, or integral with the metal tube and provided with a plurality of annular projections, on to which is fitted one end of the flexible tube. The connecting assembly further comprises a bell-type clamping element which is plastically deformed to clamp the end of the flexible tube on to the connector, so as to effect a fluid-tight seal and prevent the flexible tube from slipping off axially.
More particularly, the connector may be produced as a self-contained element by machining using a machine tool, for example by turning, or subsequently welded, for example by brazing, to an end portion of the metal tube.
However, the stage of machining by machine tool is very expensive and thus results in the connector having high productions costs.
Furthermore, this solution exhibits the drawbacks which are typical of welding, namely of treating the parts to be welded with polluting substances and the risk of the materials undergoing thermal changes.
Alternatively, the connector may be integral with the metal tube, i.e. formed by plastic deformation of the end of the metal tube on which the flexible tube is directly fitted. This solution has lower costs with respect to the previously described solution and obviates the drawbacks associated with welding but it is still not without problems.
In fact, according to a known embodiment, the connector has a main annular projection adapted to form an axial abutment for the clamping element, and a plurality of secondary projections adapted to co-operate with the flexible tube; the clamping element is deformed radially so as to form grooves interposed between said projections, which compress the flexible tube so as to ensure a fluid-tight seal and prevent it from slipping off axially. Under particularly severe test conditions, and in particular at high pulsating pressure, losses of fluid can occur as a result of leakage between the flexible tube and the connector in the region of the main projection.
The object of the present invention is to devise a duct for feeding a fluid at high pressure, which does not have the aforementioned drawbacks associated with the known art.
This object is achieved by a duct according to claim 1.
The conical profile of the main projection of the connector provides an additional compression effect of the end section of the tube adjacent the main projection, as a result of which there is achieved a substantial reduction in leakages, even under particularly severe test conditions.
According to a preferred embodiment of the invention, in which the flexible tube has a multilayer structure with an inner layer and an outer layer of elastomeric material and an intermediate reinforcing layer which is impermeable to fluid, the bell-type clamping element comprises an annular stop portion co-operating with the conical flank of the main projection and has an inner diameter which is less than the diameter of the interface surface between the inner layer and the intermediate layer of the flexible tube in the free end section of said tube.
Therefore, leakages towards the exterior are contained, which are caused by the fluid permeating through the inner layer of the flexible tube and by the permeated fluid running along the interface surface up to the end section of said tube.